OBJECTIVE: Medication-overuse headache (MOH) in cluster headache (CH) patients is incompletely described, perhaps because of the relatively low prevalence of CH. METHODS: The authors describe a retrospective series of 17 patients (13 men, 4 women) with CH who developed MOH in association with overuse of a wide range of monotherapies or varying combinations of simple analgesics (n = 9), caffeine (n = 1), opioids (n = 10), ergotamine (n = 3), and triptans (n = 14). The series includes both episodic (n = 7) and chronic (n = 10) CH patients. RESULTS: A specific triptan-overuse headache diagnosis was made in 3 patients, an opioid-overuse headache diagnosis was made in 1 patient, and an ergotamine-overuse headache diagnosis was made in 1 patient. In approximately half of the patients (n = 8), the MOH phenotype was a bilateral, dull, and featureless daily headache. In the other 9 patients, the MOH was characterized by at least one associated feature, most commonly nausea (n = 6), exacerbation with head movement (n = 5), or throbbing character of the pain (n = 5). The common denominator in 15 patients was a personal or family history, or both, of migraine. The 2 other patients gave a family history of unspecified headaches. Medication withdrawal was attempted and successful in 13 patients. CONCLUSIONS: Medication-overuse headache is a previously underrecognized and treatable problem associated with cluster headache (CH). CH patients should be carefully monitored, especially those with a personal or family history of migraine.